It is well known that an aromatic primary amine developing agent oxidized with an exposed silver halide reacts with a coupler to produce indophenol, indoaniline, indamine, azomethine, phenoxazine, phenazine or like dyes to form a dye image. In this photographic image formation system, a subtractive color process in which a color image is formed from a yellow dye, a magenta dye, and a cyan dye is used.
For cyan dye image formation, phenol cyan couplers or naphthol cyan couplers are generally employed. However, these cyan couplers have undesired absorption in the green region, causing considerable reduction in color reproducibility.
Cyan couplers which have been so far proposed to avoid this problem include pyrazoloazole couplers as disclosed in U.S. Pat. No. 4,873,183 and 2,4-diphenylimidazole couplers as disclosed in EP 249453A2. Cyan dyes produced by these couplers show reductions in their undesired absorption in the shorter wavelength side in favor of color reproduction as compared with conventional dyes. However, these couplers are still unsatisfactory in accomplishing sufficient color reproduction and their practical use results in problems requiring solution. For example, they have low coupling activity and very low stability against heat and light, or when processed with a processing solution having bleaching ability (i.e., a bleaching bath or bleach-fix bath) with a low oxidizing power or an exhausted processing solution having bleaching ability, they undergo a reduction in developed color density.
Further, U.S. Pat. No. 4,728,598 proposes pyrazoloimidazole couplers. These couplers, though exhibiting improved coupling activity, are insufficient in hue.